This invention relates to a bidirectional polymeric piston seal and, more particularly, the invention is concerned with providing a piston seal assembly that includes an E-shaped metallic spring retainer, two wound spring seal expanders and two L-shaped polymeric seals.
Heretofore, it has been common practice to provide the piston on a cryogenic refrigerator with a seal assembly which includes two C-shaped seals assembled together in a seal holder "back-to-back". These seals, because of the C-shaped design, can only be fabricated from easily machinable polymeric compounds in the small, 1/32 inch, cross sections. Because they cannot be machined from the high strength abrasive polymeric compounds, they do not have the wear life or uniform frictional resistance required for most cryogenic refrigerator applications.
The conventional C-shaped seal in the small cross sections must have the cup sections machined with a carbide tipped tool that is typically 0.010 inches wide and has a very long length dimension as compared with its width. Extreme temperatures are generated at the tip of the tool when abrasive polymeric materials have to be machined. This results in extreme tool wear such that seals in the 1/32 inch cross section cannot be manufactured economically and to close dimensional tolerances.
Thus, it would be most desirable to provide a bidirectional, polymeric piston seal assembly for a cryogenic refrigerator wherein the seal can be fabricated in the small cross section out of any of the polymeric compounds without undue tool wear and within the close dimensional tolerances required.